Textile product and process



July 25, 1967 J. M PERl I 3,332,882

TEXTILE PRODUCT AND PROCESS Filed Aug. 4, 1964 4 Sheets-Sheet 1 F I G. 1 Fl 6.2

FIG?) FIG-4 ll II II July 25, 1967 J. M. PERRI TEXTILE PRODUCT AND PROCESS 4 Sheets-Sheet 2 Filed Aug. 4, 1964 FIG. 60

July 25, 1967 J. M. PERRI 3,332,332

TE-XT'ILE PRODUCT AND PROCESS Filed Aug. 4, 1964 4 Sheets-Sheet 8 F l G. 8

so I NORHALCRIMPED FIBER. ACCEPTABLE IASH-CRIMPED m AND STEAM smsmuso FIBERS. F I G- 9 A 50 5 4o s a '5: ac E 0 Q :5 2c 60 O c u L0 2.0 3.0 TENACITY (GRAHS/ DEN.).B.0.

July 2 1967 4 J. M. PERRI 7 3,332,832

I TEXTILE PRODUCT AND PROCESS Filed Aug. 4, 1964 4 Sheets-8heet 4 VDOICTOR BLADES CRIMPED TOW OUT United States Patent "ice 3,332,832 TEXTILE PRODUCT AND PROCESS Joseph M. Perri, incompetent, Waynesboro, Va., by Pearl H. Perri, committee, Waynesboro, Va., now by decree of court to said Joseph M. Perri; assignor to E. L du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware I Filed Aug. 4, 1964, Ser. No. 387,528

9 Claims. (Cl. 161-173) This application is a continuation-in-part of application Ser. No. 242,186 filed Dec. 4, 1962, now abandoned.

This invention relates to physically modified acrylonitrile polymer fibers having improved pilling resistance while retaining characteristic durability and aesthetics. More specifically the invention provides a non-brittle fiber for durability, with a particular combination of straight tenacity and elongation at break and having controlled weak spots, whereby good pilling resistance is provided.

Most fabrics woven, knit or tufted from yarns spun from staple fibers of synthetic origin tend, during the course of wear, to form pills or clusters of fibers on the surface of the fabrics. These pills or balls of fibers are commonly anchored to the fabric by one or more filaments, and they cannot be easily removed. They give garments an unsightly appearance. It has been recognized that pilling of fabrics is due largely to a combination of the high strength and flexibility of the synthetic fibers and their smooth, 'slick surfaces. Many efforts have been made to modify synthetic fibers to improve pilling resistance. Fibers have been treated with chemicals such as hydrogen peroxide to obtain limited degradationof the fiber. Also, yarns have been made with higher twist, resinous binders have been applied, and mechanical degradation has been tried in an effort to eliminate pilling. Nylon fibers have been successfully treated with hydrogen peroxide to embrittle them at certain spots in accordance with US. Patent 3,050,822. But polyacrylonitrile is not readily reactive with hydrogen peroxide nor with acids that readily degrade most other 3,332,832 Patented July 25, 1967 have been heated sufficiently to place them in a plasticized state, crimping the plasticized filaments in the presence of a heated fluid and piddling the tow into a can. The foregoing is hereinafter referred to as mash crimping. Thereafter the crimp amplitude is lowered by stretching the crimped filaments a controlled amount in an atmosphere of steam, and thereafter chopping the filaments to staple lengths.

Understanding of the invention will be facilitated by reference to the attached drawings in conjunction with fibers may be severely damaged.

FIGURE 1 illustrates a fiber of the invention that has a knee cap shape at a cusp-type crimp;

' FIGURE 2 shows another fiber with a knee cap shape in which cracks and strain lines irradiate from the folded structure;

fibers, and efforts to carry out controlled degradation of acrylonitrile fibers in the past have been unsuccessful. Weak spots can be introduced into fibers by severe mechanical crimping. However, the fibers are erratically damaged, e.g., when crimped in a stutter-box crirnper as described in U.S. Patent 2,311,174. The entire lot of fibers is reduced in value even though only a small percentage of the fibers may be severely damaged.

It is an object of the present invention to provide acrylonitrile polymer fibers which have good resistance to pilling but retain adequate durability for long wear. Another object is to provide a process for preparing fibers in accordance with the foregoing object.

These and other objects are attained in this invention in a product characterized by low brittleness, a critical combination of tenacity and elongation-to-break values and a multitude of controlled weak spots. Low brittleness confers textile processabili-ty and end-use, durability to the product. The critical combination of tenacity and elongation-to-break and the presence of a large number of controlled weak spots result in excellent piling protection for rugs, knitwear, and other textile products manufactured from this fiber.

Preparation of this fiber is achieved by treating a bundle of uncrimped, drawn, continuous filaments which FIGURES 3 and 4 show broken ends of dyed fibers of the invention; I

FIGURES 5, 5a, 6, 6a, 7, 7a and 8 and 8a are magnified (essentially 10x) photographs with accompanying corresponding line drawings, showing cusp-type crimps in actual fibers of the invention;

FIGURE 9 is a graph showing in the enclosed area ABCDE the inter-related tenacity-elongation values; and

FIGURE 10 shows schematically a turbo-crimper that can be used for crimping in this invention.

The weak spots which are a feature of this product are located at sharp crimp bends induced by the process of manufacture. The more extensively degraded crimp bends have acusp-like shape, i.e., reversal of curvature on either side of the apex as viewed perpendicular to the fiber axis. While such cusp-like crimp bends are not entirely absent in fibers which have been crimped in the conventional manner, the frequency of this cusp-like crimp is much greater in the product of the present invention. Many of these cusp-type crimps, when viewed at high magnification EZOOX), are characterized by a knee cap on the convex side of the bend (FIGURE 1) and a multifold structure on the concave side of the bend, which has strain lines, even cracks, radiating out from this folded structure (FIGURE 2). The structure of broken ends of such crimp bends is illustrated in FIGURES 3 and 4. a

That these degraded crimp bends are the points of failure was shown by a special dyeing technique whereby the more severely degraded crimp bends are dyed selectively. This technique comprises dyeing the fiber at C. with a .007% Victoria green dye solution. This method was applied to several basic dyeable mash-crimped and steam-stretched heavier denier fibers. It was found that crimp areas similar to those just described were selectively dyed, at 70 C., particularly on the concave multifolded side of the crimp bend and along the strain lines and cracks which radiate from these folds, whereas the bulk of the fiber was only weakly stained. On the average the frequency of these dye spots was 6.2/inch in these fibers. On breaking these fibers in a microtensile tester, about of the failures occurred in the dyed portions showing that the cusp-crimp count is directly related to the frequency of weak spots in the fiber. FIG- URES 3 and 4 depict the effects just described. A high frequency in the total cusp-crimp count is therefore indicative of a high frequency of degraded bends.

The product of the present invention exhibits a sharp decrease in elongation to break with increasing length -3 of sample tested. For instance, the ratio of the breaking elongation at 0.28-inch sample length to the same quantity at 3-inch sample length is substantially greater than that for a normally crimped control.

The product of the present invention has surprisingly low brittleness characteristics in view of the extent of degradation. The reason for this is discussed hereinafter. Brittleness was measured by the reciprocal of the breaking strength at 196 C. which, in turn, is a measure of the impact strength of the fiber. This low brittleness accounts for the surprisingly good durability of which is approximately equivalent to a normal or regularly crimped fiber, of the fiber in various end-use products.

The product of the present invention is further characterized by a unique combination of tenacity and elongation not normally obtainable in acrylic fibers by simple adjustment in draw ratio and other processing conditions. Typical tenacity and elongation combinations in ordinary acrylic fibers are as follows:

TABLE I Tenacity: Elongation 1 Wet spun fiber all others are dry spun.

Hence if one attempts to weaken the fiber for improved pilling by lowering the draw ratio then the elongation increases to an unacceptable level. Since high elongation also promotes pilling the gain made in lowering tenacity is wiped out. The only exceptions to this are seen in some very low draw-ratio fiber, whose tenacity is so low 0.9 g.p.d.) that durability in end-use products is not satisfactory.

Tenacity and elongation properties (measured on boiled-off fibers in an Instron tester at one-inch gage length and 60% minute elongation rate at 25 C.) measured on satisfactory mash-crimped, steam-stretched fibers are in Table II. These properties were determined on staple fibers boiled-off as a loose mass of fibers in a cheeze-cloth bag.

TABLE II Fiber Sample D.p.f. Straight E Ten. (g./d.) (Percent) tion. Consequently a large number of fibers must be measured to obtain accurate numbers. Tensile data in this application are the average of at least 15 measurements for the liquid nitrogen breaks, and in most other cases of measurements.

The cusp-type crimp frequency counts were obtained by carefully mountingthe as-produced fibers on a microscope slide under a known tension of about 3 mg. per denier to obtain uniform crimp pull out, photographing at 10X magnification (fiber to actual photograph) and visually counting the number of cusp-type crimps per inch. FIGURES 4 to 8 show fibers having both cusp-type crimps and other types of crimp.

For fibers treated in the same manner, according to the process of this invention, the number of cusp-type crimp bends per inch will vary somewhat with denier since the number of crimps formed will depend on the slenderness ratio which, in turn, is dependent on fiber diameter (or denier). It was found that multiplication of the cusp-crimp frequency by the one-third power of denier per filament gives a number which is substantially nonvariant over a range of deniers. This number is called the cusp-crimp frequency index. For the product of the present invention, in order to achieve adequate control of pilling in use, this cusp-crimp frequency index should be greater than 7 and preferably is in the range of about 11 to 20, but may be up to 30 or even higher. Prior art products show a cusp-crirnp frequency index below 7 and in most cases below 4.

The determination of the total number of cusp-type crimps in a fiber is dependent on the magnification of the sample examined, the values increasing with increasing magnifications. Therefore it should be clearly understood that the cusp-crimp frequency index as given in this specification and claims is based on measurements made on photographs of fibers at the 10X magnification. Since there is substantial variation, perhaps infinite, in the character of the crimps present in these fibers, it should be evident that the cusp-type crimp count determination may vary from investigator to investigator. In order to remove subjectivity, as far as possible, from this determination, there are provided in FIGURES 5 through 8a photographs of fibers taken at a magnification of 10X, with a line tracing of each of the photographs. On each tracing there are short vertical lines indicating the actual crimps counted in determining the cusp-type crimp count for this invention. By projecting these vertical lines from each line filament to the corresponding filament in the corresponding photograph there can be found the cusp-type crimps to be counted. By examining the remainder of the filaments in the photographs at crimps not marked, that is, those having no vertical line on the line drawing, one can also learn the shape of crimps that are not to be counted for purposes of this invention. It must also be borne in mind that a representative sample must be taken for each determination of this and other physical characteristics and properties given in the application. It should also be realized that cusp-type crimps probably are present that are not visible because, for example, they may be evident only from a rear view of the fiber photograph, but this does not alter the validity of the index determined as indicated hereinabove.

In addition to cusp-type crimp, the fibers of the invention also contain many other types of crimp which are not readily identifiable with the more severely degraded spots. The crimp count for these other types of crimp is invariably high 10 per inch measured at 40x magnification) in the products of the present invention. These additional crimp bends probably play some role in pilling in that they inhibit migration of fibers from the inside of a yarn bundle to the fabric surface to form fuzz ends, this being the first step in the pilling process.

Anotheraspect of pilling control may be involved in control of the bicomponent crimp characteristics, in particular the crimp index (amplitude). This is measured as the difference between the extended length (ca 50 mg./ den. load) and the slack length (ca. 2 mg./ den. load) divided by the extended length and multiplied by 100. For instance, for the low denier bicomponent fiber described in Example 1 the crimp index should preferably be in the range from 6 to 12. It is an incidental benefit of the present invention that the fibers prepared by the process described hereinafter can easily be obtained with a crimp index in this desirable range.

The boiled-off elongations-to-break for different gauge lengths were computed from extreme value treatment of 50 breaks at one-inch sample length measured at room temperature and at an elongation rate of 60% per minute (see Gumbel, E. V., Statistics of Extremes, Columbia University, 1958). This provides the same type of information as would be observed from an actual measurement of breaks at various gauge lengths. From this analysis the selection of the ratio of the breaking elongation at 0.28-inch sample length (B to that at 3-inch sample length (E was taken as a'measure which best indicates the weak spot characteristics of the fiber. The product of this invention has a E /E ratio above 2.0 whereas control fibers-crimped in the normal fashion have ratios below 2.0 Preferably the product of this invention has an elongation ratio in the range of 2.5 to 10, or the range of 3.0 to 10.

As mentioned previously the product of this invention has a surprisingly low brittleness. In view of the difficulty of high-speed tensile measurements, it is preferable to measure brittleness by low temperature tensile breaking characteristics. The test procedure involves determining the breaking strength (in grams) of a one-inch long, boiled-off sample mounted in a micro-tensile tester with the sample immersed in liquid nitrogen (-l96 C.). The elongation rate is 20 percent per minute. It is Well known that fiber physical properties measured at such low temperatures are equivalent to room temperature properties measured at very high speeds.

Hence the low temperature breaks are a measure of the impact strength of the fibers. In the case of measurements on boiled-off samples, these breaks reflect the durability of the samples in end-use articles. In order to correct for large inherent differences in the various samples which include denier per filament, draw ratio, polymer composition, type of fiber (composite or homofiber) and intended end use, it is necessary to normalize the low temperature breaking strengths by dividing by the room temperature, dry-breaking strengths at low elongation rates on boiled-off fibers at 60% elongation rate and one inch gauge length. The resulting number is inverted to give a quantity (B.S. /B.S. which is a direct measure of the fiber brittleness. For good durability this brittleness number should be low; the higher the number the poorer the durability. Table III lists some a typical brittleness values for acceptable products of this invention.

TABLE III Mash-Crimped Item: Plus Steam-Stretched 1.6 d.p.f 0.58 3 d.p.f. 0.67 12.5 d.p.f 0.95 17.5 d.p.f. 0.63

All of the above products have acceptable durability. The upper limits for brittleness, as defined above, for the TABLE IV Limit Characteristics 1 Broad Preferred Most;

preferred Critical Tenacity and Elongation Wit 1m Area ABCDE in Combinations. Figure 9 Elongation Ratio (Emir E3") 2 2.5 3 Cusp-Crimp Frequency Index (OCF d.p.f. 7 11 Brittleness Number (B.S.25 o./

B.S.-1ga c.) 1.1 0.9 0.7

1 As described in above text; Cusp-Crimp Index on as-produced fibers; others on boiled-01f sample.

The fibers of this invention may be from either homopolymers of acrylonitrile or copolymers of at least of acrylonitrile with other monomers such as methyl acrylate, sodium styrene sulfonate, vinyl acetate, vinyl pyridine, methyl vinyl pyridine, methyl methacrylate, styrene, acrylamide, etc. These may be either spun as simple homofibers or as side-by-side composite fibers. It is possible to use the fibers of this invention in the form or (particularly in rugs) to blend them with an undegraded fiber of low draw ratio and higher denier. This is illustrated in the examples.

Preparation of this fiber can be achieved by treating a bundle of uncrimped, drawn, continuous filaments which have been heated to place them in a plasticized state, mash-crimping the plasticized filaments in the presence of a heated fluid, lowering the crimp amplitude by stretching the crimped filaments a controlled amount in an atmosphere of steam, and thereafter chopping the filaments to staple lengths. Individually these process steps are well 'known and details of their practice, and apparatus therefor, may be found in the published technical literature.

In carrying out the process, the drawn, continuous filaments can be heated to a temperature in the range from about 70 C. to about 78 C., preferably in an atmosphere of steam, to place them in a plasticized condition. The filaments are forwarded in the plasticized state to a stiffer-box crimper to which steam at a pressure from about 10 to about 25 pounds per square inch gauge, is continuously introduced to maintain a temperature within the crimper between about 90 C. and C. A stuffer-box crimper of the type described in U.S. Patent 2,575,781, or of similar 'dcsign in which transverse crimping pressures, i.e., transverse to the longitudinal axis of the filaments, in the range between about 10 and 80 pounds per square inch are applied by the clapper mechanism, may be used. Crimping pressures in the range from about 40 to 80 pounds per square inch are preferred. Clearances in the feed rolls to this particular stuffer-box are critical and should be maintained between about 0.001 inch and 0.01 inch with an optimum close to 0.006 inch for 335,000 denier rope or tow. The crimped tow is then piddled into a tow cart in the usual way.

Under the crimping conditions just described, all of the filaments are severely crimped. The severe crimping reduces the dry straight tenacity and elongation. While this has the desirable result of placing the combination of the tenacity-elongation values of the fiber into Area ABCDE of FIGURE 9 and thus results in good pilling protection, this change in fiber physical properties is accompanied by an unacceptable decrease in the impact breaking strength as measured by low speed breaks in liquid nitrogen. The percentage decrease in the low temperature breaking strength is actually substantially greater than the percentage decrease in the room temperature breaking strength and thus the brittleness number of the fiber becomes unacceptably large, that is, larger than 1.1. Rugs made from these mash-crimped fibers have poor durability which is related to the low impact strengths of the boiled-off fibers. The crimped filaments, however, are surprisingly improved in their ability to withstand these impact forces if they are stretched in steam a controlled amount.

Another way to mash-crimp the filaments is to use a modified Turbo-crimper (Model CC made by Turbo Machine Works). A schematic diagram of a portion thereof is shown in FIGURE 10. For purposes of the present invention, doctor blades 20 and 22 are adjusted to narrow the throat 24 at the entrance to the stuifer box and extend it to within 0.004 inch of the crimper rolls 26 and 28. One-quarter inch wide crimper rolls are used. Steam lines (not shown) are provided to feed steam to the tow at the input side of the crimper rolls to plasticize the product. A steam line (not shown) is also connected to the stutfer box. With this type crimper, smaller amounts of steam are needed since the tow size is small (10,000 to 25,000 denier). It is not absolutely necessary to feed steam into the crimper box but it is usually advisable to do so for best results. The usual steam pressures used in the preheat line are in the 1 to 3 p.s.i.g. range and those in the crimper box from to 4 p.s.i.g. Crimper roll settings of about 300 to 500 and clapper settings from 180 to 300 may be used. The exact settings will depend on the condition of the equipment and the type of fiber being processed. Operating speeds in the 50-100 y.p.m. range are used. Steam stretching is done in a manner analogous to that discussed hereinafter.

To accomplish steam-stretching, the tow is pulled from the tow can through tensioning bars and a steam chest to steam stretch it. The amount of stretch required will depend on the degree of mash crimping and on the fiber properties required. The stretch is defined as the difference between the output speed from the steam chamber and th input speed to the chamber divided by the input speed and multiplied by 100 to convert to a percentage basis. The range of stretch may vary from to 75% with an optimum of about and is achieved by control of the output speed from the chest relative to the speed of the tow fed from tow cans through tensioning bars to the chest. This amount of stretching is enough to reduce the crimp amplitude without causing fiber drawing, or denier decrease.

The conditions under which the crimp amplitude is reduced involve exposing the tow to steam for at least about 0.2 second and preferably from about 0.6 to 3.0 second. The speed at which the filaments are passed through the atmosphere of steam, i.e., a steam chest, will, of course, depend on the dimensions of the chest. The steam in the chest is maintained at atmospheric pressure and is introduced from a super-heated steam source at a rate from about 0.1 to about 1.0 pound of steam per pound of filaments. Preferably from about 0.20 to about 0.55 pound of steam per pound of filaments is used. After the crimped filaments have been stretched, they are cooled and cut into staple lengths and dried in the usual manner.

This steam-stretching operation results in a selective increase in the low temperature breaking strength without any substantial change in the room temperature breaking strength; consequently, the brittleness number is decreased into the acceptable range of 1.1 or below. Thus articles TABLE V Item 1 Mash-crimped Mash-Orirnped and Steam-Stretched 1 AA 1.6 d.p.t., 6X draw ratio bicomponent fiber made from Side I, 50 parts of a mixture of 90 parts of aerylonitrile homopolymer and 10 parts of a copolymer of 96% acrylonitrile and 4% of sodium styrene sulfonate, and Sid? II, 50 parts of a copolymer of 91.3% acrylonitrile and 8.7% of vinyl ace a e.

BA 12.5 d.p.i., 3.65X draw ratio bicomponent fiber made from: Side I, 57 parts of a eopolymer of 96% aerylonitrile and 4% sodium styrene sulfonate, and Side II, 43 parts of a mixture containing 90 parts of acrylonitrile polymer and 10 parts of the polymer of Side I.

OA 17.5 d.p.f., 3.03X draw ratio fiber similar in composition to the fiber in Example II.

Another problem encountered with fibers which have been mash-crimped is that it is virtually impossible to process them. However, surprisingly, steam-stretching overcomes this deficiency. While boiled-off properties are to be used in any consideration involving durability under end-use conditions, as-produced properties are relevant to processing the fibers. It has been found that the asproduced properties of mash-crimped fibers are too low to allow textile processing. For instance, the fibers give high losses during the carding operation involved in the yarn-making process and also give weak yarns. Contrary to the negligible change observed in the room temperature, boiled-off properties, steam stretching improves the as-produced, room temperature properties to a very substantial degree. For instance, tenacity (measured at room temperature at 60% per minute elongation rates on oneinch samples in an Instron machine) is improved by a factor of about 1.4. The increase in elongation is even more dramatic ranging from a factor of 1.9 to a factor of 3.7 for several diiferent items. This is illustrated in Table VI and explains the improved yarn strength and carding performance that result from steam-stretching.

1 As-produced state. 2 Same as described in Table V.

In addition to providing the necessary improvements of reduced fiber losses on carding and durability in use, steam-stretching provides two other benefits. It opens up the structure of the rope in a manner which breaks down any semi-fused sections where the interfiber forces are strong. This is essential to provide good opening before and during carding. The second advantage is that the lower crimp amplitude and reduced sharpness in the crimp bends very materially afiects the handle of the various end-use articles such as knitwear and rugs. Specifically it reduces the harshness from an unpleasant to a highly desirable handle. Indeed the degree of stretch can be modified in some cases to optimize handle to fit the aesthetic requirement of various end-uses. The degree of latitude in stretch available for handle control is limited only by the acceptability of the pilling and durability performance of the end-use item in question.

In summary typical limits of the process just described that provide the product of this invention are shown in the following table.

1 For a stutter-box crirnper of the type describedin U.S. Patent 2,575,781 and a tow size of about 335,000 denier; different designs may require adjustment in process limits.

The invention will be described further in conjunction with the examples that follow, wherein details are given by way of illustration and not by way of limitation.

Except where otherwise specified, in the examples a steam chest which was eight feet long was used. The filament bundle (tow) was passed through this at rates listed in the examples with the opitmum rate being around 200 y.p.m. This represents a residence time of 0.80 second in the atmospheric steam used. Temperature in the steam stretching cell was li5 C., rope temperature was 95i-5 C., and .24 lb. per steam 1b. of fiber was employed. The fiber bundle is passed through overhead tensioning bars and pulled through the 8 ft. long steam cell at the indicated rates of speed. The amount of stretch in the chest is specifiedin the examples. .The fiber then goes directly to cutting and drying operations.

Tests mentioned in the examples are as follows: Pilling of knitwear was carried out in what is called the Random Tumble Pill Test (see ASTM D-1375, ASTM Standards 1958, Part 10, page 510). Rug fiber pilling is determined by a rather analogous test and subjective ratings are applied.

Durability testing for knitwear was measured as the percent weight loss as a function of time on the Taber Abrasion Tester; see ASTM D-l175-Rotary Platform Double Heat Method, ASTM Standards 1961, Part 10, p. 465.

Example I Side-by-side bicomponent fibers are spun, from solutions in dimethylformamide, from 'two different polymer compositions in a 1:1 ratio, under spinning conditions to result in filaments predominantly of longitudinally divided cross-sections. Such cross-sections are generally elliptical and the interface of the polymer components is disposed along the major axis of the ellipse. (See FIG. 4 ofTaylor, No. 3,038,237, and the patent generally for spinning equipment and methods.) The compositions comprise: (I) 91.3 parts of acrylonitrile and 8.7 parts of vinylacetate; and (II) 90 parts of the homopolymer of acrylonitrile and 10.0 parts of a copolymer containing 96 parts of acrylonitrile and 4 parts of sodium styrene sulfonate. The resulting fibers are drawn 6X to a 24,000 denier tow. The tow is passed through a Turbo-crimper discussed above at a speed of 66 y.p.m. Steam is fed onto the tow at 1 /2 p.s.i.g. as it enters the crimper, and is fed to the crimper at 2 p.s.i.g. The crimper rolls are set at 350 and the clapper setting is 180. From the crimper the tow is piddled into a can, and subsequently subjected to a steam stretching operation. In the steam stretching step, the tow is pulled out of the can through several tensioning bars and a steam chest. The tensioning bars are adjusted so that the output speed from the steam chest is 1.25 times the input speed to the steam chest. The steam temperature in the chest is C. The output speed from the steam box is 223 yards per minute giving a 0.72 second residence time. Steam consumption is 0.24 pounds per dry pound of fiber. The fiber is then fed directly from the steamer to a cutter (1 /2 inch cut length) and then dried. Fiber properties determined on fibers similarly prepared are as follows:

1 Measured on boiled-01f fibers at the breaking point in an Instron Tester at 60%lmin. elongation rate at room temperature with 1 inch gage length.

2 See test description in preceding text.

3 After 20 minutes in a Random Tumble Pill Tester where 5.0 represents no pilling and 3.0 is acceptable.

This tenacity and elongation balance in the mashcrimped product cannot be achieved in normal processing (see Table I) and is within the acceptable area defined by Area ABCDE of FIGURE 9. The brittleness number (BS /B.S. the elongation ratio, and cuspcrimp frequency index are all within the limits specified for this product. The reduction in crimp index which occurs as a result of the process of this invention probably aids in achieving the good pill resistance.

This fiber cards well on a standard cotton card and is spun into 20/1 cc. 13.4Z t.p.i. yarn. Before steam-annealing, the mash-crimped fiber cards very poorly. The yarn is knit into 4.5 oz./yd. jersey-knit fabrics and tested for pilling. The control pills badly whereas the test item is pill resistant. Durability of the fabric made from the treated fiber is equivalent to a control as measured by Taber Abrasion Tests.

Example I] A fiber of a copolymer of 93.65% acrylonitrile, 5.98% methyl acrylate, and 0.37% sodium styrene sulfonate is spun from a 29% solution in dimethylformamide, to which 5.2% (based on the solids) of tris 2,3 dibromopropyl phosphate is added, into a hot, gaseous environrnent to form a tow of filaments. The tow is drawn 3.03 x in hot water to remove traces of solvent and orient 'the molecular structure to give a final rope denier of 335,000. After drawing, the tow is crimped by passing it through a steam pre-heater to plasticize the product and it is then fed into a stutter-box crimper (see US. Patent 2,575,781). The tow is cut to 4 inch cut length and dried. The crimping conditions for the normal crimped control and the mash-crimped items are shown below. The steam stretching is done using the same equipment and conditions described in Example 1. The fiber properties and key process parameters are shown in Table IX.

TABLE IX Treated Fiber Normal Mash- Item Crimped Mash- Crimped and Control Crimped Steam- Stretched Mash-Orimping Process Conditions:

Rope temperature C.) 69 70 70 Stam Pr)essure in Supply to Stufter-B ox 9 15 p.s.1.g

Clapper Pressure (p.s.i.g.) 45 45 Feed Roll Clearance (in.) 020 006 006 Speed (y.p.m.) 175 175 175 Fiber Properties:

Tenacity, Straight (g.p.d.) 1.49 1. 18 1.14

Elongation, Straight (percent)- 61. 7 23. 1 26. 8

Elongation Ratio (EMB /Ey 1. 5 6. 6 8. 2

Cusp-Crimp Frequency Index(COFXd.p.f. 2. 5 13. 7

Brittleness Number (B.S.z c, /B.S.-19e c.).- 1. 15 0. 61 End Use Properties:

Pilling (40 hrs.) Poor Acceptable Acceptable Durability (hours in Tumble Tester to Good Poor Good both plies cut through) The boiled-01f, mash-crimped, steam-crimped, steamstretched fibers exhibit a range of properties well Within the limits used to describe this product. Tenacity and elongation are within Area ABCDE defined for an acceptable product in FIGURE 9. The elongation ratio and brittleness number fall within the most preferred limits. The cusp-crimp frequency index on the as-produced fiber is also above the preferred limit. The mash-crimped, steam-stretched fibers are processed on a conventional woolen card with no excessive losses and good operability to make a 1.25 w.r. (4.5Z t.p.i.) yarn. Thi yarn is twoplied at 35 t.p.i. and tufted to a oz./yd. carpet at 7 gage and A pile height. The test data confirm the excellent pilling and durability performance of the rugs made from the steam-stretched fiber. The durability is equivalent to that for a regular crimped control whereas pilling is much improved over the regular crimped control.

The beneficial effects of steam-stretching on durability are seen in the data in Table IX. This is explained by the lower brittleness of the steam-stretched item. The asproduced, mash-crimped fiber suffered heavy losses on carding, did not open well, and gave weak yarns. After steam-stretching, the fibers processed well to give strong yarns. Fiber data listed below (Table X) show differences in as-produced properties before and after steamstretching which explain this surprising improvement in yarn processing and yarn properties on steam-stretching.

b fAs-produced state-measured on Instron tester as indicated hereine ore.

Example III A bicomponent fiber is spun from two different polymer compositions in side-by-side relationship along the length of the fiber according to the process in US. Patent 3,038,237. The compositions were as follows: (I) 57 parts of a copolymer described as follows: 96 parts of acrylonitrile and 4 parts sodium styrene sulfonate; (II) 43 parts of a mixture composed of: 90 parts of an acrylonitrile homopolymer and 10 parts of a copolymer containing: (a) 96 parts of acrylonitrile (b) 4 parts of sodium styrene sulfonate. These compositions as solutions in dimethylformamide containing 6 percent of tris-2,3-dibroinopropyl phosphate are cospun and the fibers are drawn 3.65 In the form of a 335,000 denier tow, the fibers are passed through a steam chamber where the tow is heated to to 72 C. with wet steam. The tow is then passed into a standard stuifer-box crimper as described in US. Patent 2,575,781. A high clapper pressure, 52 psi. gage, is used, and steam is passed into the stuffer-box during crimping from a steam line having a pressure of 14 psi. The clearance between the rolls of the crimper is 0.006 inch. After crimping, the rope is stretched 25% as described in Example I. It is cut to 3%" cut length and dried in a conventional manner. This fiber will be referred to as Fiber A.

Fiber A is blended with a homofiber referred to as Fiber B, which is spun from a copolymer containing 93.65% acrylonitrile, 5.98% methyl acrylate, and 0.37%

sodium styrene sulfonate, containing 6% of tris-2,3-di-.

bromopropyl phosphate (based on total solids). This fiber is drawn 2.12 and cut into 4-inch staple and dried in the usual manner.

Key properties, determined a indicated in Table VIII, of these two fibers are shown in the following data:

For the mash-crimped, steam-stretched Fiber A, tenacity and elongation levels have been lowered to acceptable values and the cusp-crimp frequency index, elongation ratio, and brittleness number are all in an acceptable range. With the exception of brittleness, all normalcrimped Fiber A properties are outside the limits characterizing the products of this invention.

The mesh-crimped and steam-stretched Fiber A and Fiber B are blended in equal amounts and are then spun with good performance on the card to a 1.25 w.r. fiber and twisted 4.5Z t.p.i. The yarn is two-plied and tufted to make a 25 oz./yd. carpet having 7 greige pile height. It is then piece dyed in the Beck. It is tested for pilling and durability and found to be fully satisfactory on both counts. A blend with the normal crimped Fiber A pills badly.

13 14 As in the preceding example, Fiber A is much stronger after steam-stretchingg as illustrated by the data in Table TABLE XIV XII; hence it gives better processing performance on the card and stronger yarns than in the case of the same item 32 1 gag; before steam-stretching. 5 Crimped Mash- Item and Crnnpe Steam plus Stretched Steam TABLE XII Stretched Mash- D.p f 12. 5 12. 5 Item Mash- Crimped l0 Tenac1ty.st., (g.p.d.) 1.07 1.44 Crimped and Steam- Elongat on, St., (pBIC8Ht) 34 44 Stretched Elongation Ratio (Thaw/E3") 3. 9 1. 8 Cusp-Crimp Frequency Index (QCFXd.p.f. 11.4 10.2 Elongation, Straight (percent) 1 17.8 3. 97 Pllllng 1 Poor Tenacity, Straight (g.p.d.) 1 1.08 1. 41

' E Rug1 up?) a 1:1 blend with a low draw ratio fiber (like Fiber B in 1 t t xamp e Measured in the as produced 5 a e 2 Acceptable to Good.

Ex 1 From the foregoing discussion and description it is evident that the invention provides fibers comprising A S eI'ES Of 1.6 d.p.f. composite fibers similar to the one acrylonitrile having unique and highly desirable Chan descnbed a I are mash'cnmped and a acteristics. While the invention has been described with stretched glve Vanous fig of spot Weakemnfrespect to specific materials and details, it should be ap- These various fibers are spun into 20/ 1 cc. (13.42 t.p.1. parent that changes can be made without departing from tll/1st) Y 115mg conventlonal Cotton card and are 25 its scope. It should further be evident that the spinning then knit With 3. jersey SilltCl'l t0 make 4.5 OZ./yd. finlshed methods, polymer compositions, fiber denier and cross- (dyed) fabrics. The data obtained are: sections and the ilke heretofore characteristic of the art TABLE XIII E, Cusp- Item Type of Crimp '1 (g.p.d.) Percent E0.23"/E3" Freq. Filling Index 1 Regular crimp 3.2 24.8 1.28 2.6 0 2 Insufiicient mash-crimp plus steam-stretch 2.82 25. 7 1. 56 6. 5 1 3 do 2. 37 22. 5 1.80 30. 5 2 4 Good mash-crimp plus 1.64 15.0 2.56 14.1 3

steam-stretch. 5 do 1.68 17. 5 2. 59 15. 3 3

1 Random Tumble Pill Test where 5.0 is perfect and 3 is acceptable (results rounded 011 to nearest 0.5).

Items 1 and 2 are clearly unacceptable in all properties and pill badly. Item 3 is actually way above acceptability limits in cusp-crimp frequency index and is barely in limits of Area ABCDE on the tenacity-elongation plot of FIGURE 9. The unsatisfactory pilling of the item 3 is attributed solely to the unacceptably low elongation ratio. This illustrates the fact that the three product characteristics specificed in this invention for pilling protection must be met simultaneously. Items 4 and 5 are within all acceptability limits and give satisfactory pilling protection.

Example V Two heavy-denier composite rug fibers identical to the composition of Fiber A in Example III but differing in that one is mash-crimped according to the process of this invention whereas the other is mash-crimped under conditions which result in inadequate spot weakening, are provided and tested. The data below show that the insufficiently mash-crimped product pills, in rugs, and is outside the preferred limit of cusp-crimp frequency index and outside the acceptable limits of the elongation ratio although it is within Area ABCDE on the elongation-tenacity plot in FIGURE 9. This, too, illustrates the importance of the unique combination of all the specified properties and physical characteristics in the products of the invention. The fiber that is mash-crimped according to the practices of this invention gives good pilling reof acrylic fibers can be used in conjunction with this invention unless otherwise indicated or apparent. The term as-produced in the specification and claims means the state of the fiber upon mash-crimping and steam-stretching but before boil-off treatment of any kind. Boil-off procedures known in the art generally can be applied to the products of this invention and it can be practiced as a particular operation or in conjunction with dyeing or otherwise.

What is claimed is:

1. As an article of manufacture, a durable pill resistant highly crimped fiber having a multiplicity of weakened areas along its length at the crimp bend, and composed of at least one polymer consisting essentially of to weight percent of acrylonitrile and 0 to 15 weight percent of monomer copolymerizable with acrylonitrile, the fiber being structurally characterized in the as-produced state by cusp-type crimp along its length in number such that its cusp-crimp frequency index is at least 7, and exhibiting in the boiled-off state a combination of values of tenacity and elongation to break within the area ABCDE of FIGURE 9, an elongation ratio of at least about 2 and a brittleness number less than about 1.1.

2. An article according to claim 1 in which the elongation ratio of the fiber is in the range of 2.5 to 10.

3. An article according to claim 2 in which the brittleness number of the fiber is less than 0.9, and the cuspcrimp frequency index is in the range of 11 to 20.

4. An article according to claim 1 in which the brittleness number of the fiber is less than 0.7.

5. An article according to claim 4 in which the elongation ratio of the fiber is in the range of 2.5 to 10.

6. An article of manufacture comprising a durable, pill resistant mash-crimped fiber having a multiplicity of weakened areas along its length at the crimp bend and composed of at least one polymer consisting essentially of 85 to 100 weight percent of acrylonitrile and 0 to 15 weight percent of monomer copolymerizable with acrylonitrile, the fiber being structurally characterized in the as-produced state by cusp-type crimp along its length in number such that its cusp-crimp frequency index is 11 to 20, the fiber in the boiled-01f state having a combination of values of tenacity and elongation to break within the ABCDE area of FIGURE 9, an elongation ratio within the range 2.5 to 10 and a brittleness number of about 0.3 to 0.9

7. A pill resistant staple fiber according to claim 6.

8. A tow comprising fiber according to claim 6.

9. A method comprising heating a bundle of fibers comprising at least one polymer consisting essentially of 20 References Cited UNITED STATES PATENTS 2,686,339 8/1954 Holt 19--66 2,766,505 10/1956 Weiss 57-l40 3,020,700 2/ 1962 Van Dijk 28-72 3,022,565 2/1962 Fitzgerald 2872 3,078,542 2/ 1963 McFarren et a1 l966 ALEXANDER WYMAN, Primary Examiner JACOB STEINBERG, Examiner.

M. A. LITMAN, Assistant Examiner. 

1. AS AN ARTICLE OF MANUFACTURE, A DURABLE PILL RESISTANT HIGHLY CRIMPED FIBER HAVING A MULTIPLICITY OF WEAKENED AREAS ALONG ITS LENGTH AT THE CRIMP BEND, AND COMPOSED OF AT LEAST ONE POLYMER CONSISTING ESSENTIALLY OF 85 TO 100 WEIGHT PERCENT OF ACRYLONITRILE AND 0 TO 1K WEIGHT PERCENT OF MONOMER COPOLYMERIZABLE WITH ACRYLONITRILE, THE FIBER BEING STRUCTURALLY CHARACTERIZED IN THE AS-PRODUCED STATE BY CUSP-TYPE CRIMP ALONG ITS LENGTH IN NUMBER SUCH THAT ITS CUSP-CRIMP FREQUENCY INDEX IS AT LEAST 7, AND EXHIBITING IN THE BOILED-OFF STATE A COMBINATION OF VALUES OF TENACITY AND ELONGATION TO BREAK WITHIN THE AREA ARCDE OF FIGURE 9, AN ELONGATION RATIO OF AT LEAST ABOUT 2 AND A BRITTLENESS NUMBER LESS THAN ABOUT 1.1. 